It would take me time to find the quantifying explanation, but a grain/feed being "hot" does NOT mean that it heats up the bird/animal that ingests it... It just means that it provides more "usable" calories than other food stuffs, is more easily/readily digestable, provides more usable nutrition for the bird/animal. Corn is another "hot" grain and when folks hear that, they get the misconception that they should not feed it in hot weather for fear of overheating/killing their birds. I don't know what breed birds you have and how well they are adapted to heat... I understand it has been exceptionally hot over there on the west coast this summer... Like more than normal for the desert even. I'm sure they are acting "hotter" than normal...
Are your birds free ranging or inside an enclosure? Do they have free and easy access to "cool" water and shade? Normal birds will lessen the amount they eat when it gets real hot and eat more when it gets cold. They self regulate pretty darned well... better than a lot of us humans
<---speaking for myself there... You say it was young rooster(s)? How young? perhaps something physically wrong with them? You said you have like 150 young birds... 2 out of 150 is a very low mortality rate. Hard to say what might have caused the deaths but it's highly unlikely that it was the FF as the rest of your flock is just fine... right? Could they have hurt themselves somehow, or possibly an altercation with another bird? Did you look over the carcass for any evidence of external damage?
Sorry you lost them, but again, I can't see that it was the FF.